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A 25-year dynamic ecological analysis of psychiatric hospital admissions and prison committals: Penrose’s hypothesis updated

  • C. J. O’Neill (a1), B. D. Kelly (a2) and H. G. Kennedy (a1)

There is renewed interest in the inverse association between psychiatric hospital and prison places, with reciprocal time trends shown in more than one country. We hypothesised that the numbers of admissions to psychiatric hospitals and committals to prisons in Ireland would also correlate inversely over time (i.e. dynamic measures of admission and committal rather than static, cross-sectional numbers of places).


Publicly available activity statistics for psychiatric hospitals and prisons in Ireland were collated from 1986 to 2010.


There was a reciprocal association between psychiatric admissions and prison committals (Pearson r=−0.788, p<0.001), an increase of 91 prison committals for every 100 psychiatric hospital admissions foregone.


Penrose’s hypothesis applies to admissions to psychiatric hospitals and prisons in Ireland over time (dynamic measures), just as it does to the numbers of places in psychiatric hospitals and prisons in Ireland and elsewhere (static, cross-sectional measures). Although no causal connection can be definitively established yet, mentally disordered prisoners are usually known to community mental health services. Psychiatric services for prisons and the community should be linked to ensure that the needs of those currently accessing care through prisons can also be met in the community.

Corresponding author
*Address for correspondence: Professor H. G. Kennedy, National Forensic Mental Health Service, Central Mental Hospital, Dundrum Road, Dublin 14, D14 W0V6, Ireland (Email:
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Irish Journal of Psychological Medicine
  • ISSN: 0790-9667
  • EISSN: 2051-6967
  • URL: /core/journals/irish-journal-of-psychological-medicine
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